Hydrologic Changes Drove the Late Miocene Expansion of C_4 Grasslands on the Northern Indian Subcontinent

Pratigya J.Polissar; Kevin T.Uno; Samuel R.PhelpsAllison T.KarpKatherine H.FreemanJennifer L.Pensky

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Hydrologic Changes Drove the Late Miocene Expansion of C_4 Grasslands on the Northern Indian Subcontinent

机译：Hydrologic Changes Drove the Late Miocene Expansion of C_4 Grasslands on the Northern Indian Subcontinent

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Modern tropical and subtropical C_4 grasslands and savannas were established during the late-Miocene and Pliocene,over 20 Myr after evolutionary originations of the C_4 photosynthetic pathway.This lag suggests environmental factors first limited and then favored C_4 plants.Here,we examine the timing and drivers for the establishment of C_4 grasslands on the Indian Subcontinent using carbon and hydrogen isotope signatures of plant-wax n-alkanes recovered from turbidites in the Bengal Fan.Like prior studies,we find C_4 ecosystems in the Ganges-Brahmaputra catchment first emerged at 7.4 Ma and subsequently expanded between 6.9 to ~6.0 Ma.Hydrogen isotope values varied from 10.2 to 7.4 Ma and then increased after 7.4,which suggests intermittent drying began before the establishment of C_4 grasslands with further drying at the onset of C_4 expansion.Synthesis of published plant fossil data from the Siwalik Group of the Himalayan foreland basin documents an ecosystem trajectory from evergreen tropical forests to seasonally deciduous forests,and then expansive C_4 grasslands.This trajectory coincided with a seasonally uneven drying trend due to both increased evaporation of plant leaf and soil waters and reduced rainfall,as identified in soil carbonate and tooth enamel data sets.Collectively the fossil,biomarker,and isotopic evidence reveal the development of modern C_4 ecosystems on the Indian Subcontinent followed a series of ecosystem transformations driven by drying and fire feedbacks,and possibly declining atmospheric pCO_2,beginning at 10.2 Ma and strengthening through the late Miocene.

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《Paleoceanography》 |2021年第4期|e2020PA004108-1-e2020PA004108-22|共22页
作者
Pratigya J.Polissar; Kevin T.Uno; Samuel R.PhelpsAllison T.KarpKatherine H.FreemanJennifer L.Pensky;
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Division of Biology and Paleo Environment,Lamont-Doherty Earth Observatory of Columbia University,Palisades,NY,USA;

Department of Geosciences,The Pennsylvania State University,University Park,PA,USA;

Department of Ocean Sciences,University of California,Santa Cruz,Santa Cruz,CA,USABarnard College,New York,NY,USA;

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中图分类海洋学;
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Hydrologic Changes Drove; Late Miocene Expansion; Grasslands;

Hydrologic Changes Drove the Late Miocene Expansion of C_4 Grasslands on the Northern Indian Subcontinent

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